Lecture 3 - overview of methods Flashcards
How do we classify neurons?
- structure
- gene expression
How do we base the structure of neurons to classify them?
- number of neurites
- dendritic geometry - unipolar, bipolar & multipolar
- connections - where do they project?
- axon length
How do we base gene expression of neurons to classify them?
- underlies structural differences
- defines neurotransmitter expression - e.g. excitatory vs inhibitory neurotransmitters
This is useful as neurons can be identified, which reduces the need for tracing of each neuron individually.
What is a ganglia?
clump of cell body in the peripheral system
What is the role of dorsal root ganglion?
transmit signal from sensory receptors, however it becomes a dendrite. Signal carried to spinal cord.
- the lack of branching means it is RELIABLE at transferring information
How many neurites do dorsal root ganglion have?
1 - unipolar
Describe the properties of bipolar neurites
- small area for receiving synaptic input = highly specialised function
- reliable relay of information
- retinomal bipolar
Describe the properties of multipolar neurites
- can receive about 150,000 connections
- majority of neurons in the brain
- large area for receiving synaptic input
- high levels of convergence
- involved in motor control
What are the 2 types of dendritic geometry?
- Stellate
- Pyramidal
Describe stellate dendritic geometry
star shaped dendritic arbour
Describe pyramidal dendritic geometry
- distinct APICAL & BASAL dendritic trees
- pyramidal shaped soma
- found in the cerebral cortex
Where do sensory neurons project to?
afferent
Where do motor neurons project to?
efferent
What are 2 types of interneurons?
- relay or projection neurons
- long interneurons
What do relay or projection neurons do?
- connect brain regions
- can be quite long
What do local interneurons do?
- process information in local circuits
- short axons
What allows investigation into where neurons and what they are doing?
manipulation of neuron genetics can lead to fluorescence (inclusion of gene/promoter region) or knocking out a gene
What acts as nerve glue and fills the space around neurons?
Glia
- extracellular space of approx. 20um between glia & neurons
- can proliferate throughout life
Can glia cells regenerate?
yes - whereas neurons can’t in lots of regions
What are glial cells found in the CNS involved in homeostasis called?
astrocytes
What are glial cells found in the PNS involved in homeostasis called?
satellite cells
What are glial cells in the CNS involved in myelinating cells called?
oligodendrocytes
What are glial cells in the PNS involved in myelinating cells called?
Schwaan cells
What are glial cells in the CNS that act as phagocytic cells?
microglia
What are glial cells in the PNS that act as phagocytic cells?
Schwaan cells & macrophages
What are astrocytes?
- control environment surrounding neurons
- spatial domains
- unique marker - glial fibrillation acidic protein (GFAP) - immunohistochemistry can be used to visualise astrocytes
- many subtypes
How do astrocytes as fuel suppliers?
- glycogen stores of the brain
- 5-10 minutes supply
- metabolise glycogen & supply lactate
- endfeet rake up glucose
What occurs during times of lower glucose levels?
neurons may use the glycogen stores in astrocytes to create ATP.
What does the tripartite synapse do?
- terminates neurotransmitter activity
- recycles neurotransmitter to presynaptic terminals
- astrocytes have receptors too
What makes up the tripartite synapse?
- presynaptic terminal
- dendrites
- glial cells (astrocytes)
What are other roles of astrocytes?
- buffer extracellular potassium
- form part of the blood brain barrier
- couple neuronal activity to blood supply
What is microglia?
macrophages of the CNS (phagocytic)
- can be in an active or inactive form
- key role in tissue surveillance & phagocytosis
- many more roles - emerging field
- can have harmful roles in neurodegenerative diseases
What do oligodendrocytes do?
- myelinating oligodendrocytes from myelin sheaths of CNS axons
- can have 15-30 projections from cell body to myelin sheath
What do Schwaan cells do?
- form myelin sheaths of PNS (peripheral nervous system)
- one Schwaan cell provides one myelin segment to a single axon
Describe the formation of myelin sheath
- process of oligo cytoplasm
- wraps many times around the axon
- cytoplasm squeezed out of layers by COMPACTION - left with membrane
- myelin still a living component - mainly made of membrane
Why do myelin sheaths maintain contact glial cells?
for nourishment
What is the function of myelin?
- myelination is insulating & creates nodes of Ranvier enabling saltatory conduction
